Recently, in view of preventing global warming, it has been required to reduce emissions of carbon-dioxide, which is considered as one of the causes. Then, it has been investigated to use a blended fuel of liquid hydrocarbon such as gasoline and ethanol as fuel for motor vehicles.
As the ethanol of the blended fuel, if bioethanol obtained by fermentation and distillation of a plant substance e.g., an agriculture product, such as sugar cane and corn is used, it is considered that a so-called carbon neutral effect can be obtained. The carbon neutral effect means that if a substance derived from a plant is used as bioethanol, when the ethanol is burned the net carbon dioxide emission theoretically becomes zero. This is because the amount of carbon dioxide discharged in the air by combustion of bioethanol is equal to the amount of carbon dioxide absorbed by a plant itself serving as a raw material from the air.
Therefore, if bioethanol is used in place of liquid hydrocarbon such as gasoline, carbon-dioxide emissions can be reduced by the amount of bioethanol.
However, if sugar cane, corn and the like are used as a raw material for ethanol in a large amount, the amount of them supplied as food reduces. This is a problem.
Then, a technique for producing ethanol by using nonedible lignocellulose biomass in place of a plant substance such as sugar cane and corn has been investigated. The lignocellulose biomass contains cellulose. If the cellulose is decomposed by enzymatic saccharification into glucose and the obtained glucose is fermented, bioethanol can be obtained. Examples of the lignocellulose biomass include wood, rice straw, wheat straw, bagasse, bamboo, pulp and waste materials (e.g., used paper) produced from these.
However, lignocellulose contains hemicellulose and lignin other than cellulose as major components. Usually cellulose and hemicellulose are tightly bound with lignin. As the result, an enzymatic saccharification reaction to cellulose is inhibited by lignin. Thus, to perform the enzymatic saccharification reaction of cellulose, lignin is desirably removed in advance.
For this purpose, an apparatus for pretreatment for saccharification of lignocellulose biomass is known in which the lignocellulose biomass is mixed with liquid ammonia and then the pressure is rapidly reduced to expand gas of liquid ammonia, thereby expanding the biomass to remove lignin from the biomass (see, for example, Patent Literature 1).
Such a conventional apparatus for pretreatment for saccharification of lignocellulose biomass has a mixing unit, a heating unit, a discharge means and a recovery unit.
In the conventional apparatus for pretreatment for saccharification of lignocellulose biomass, lignocellulose biomass and liquid ammonia are mixed by the mixing unit to obtain a biomass-ammonia mixture. Subsequently, the biomass-ammonia mixture is heated by the heating unit and ammonia is discharged while being pressurized and compressed by the discharge means so as not to evaporate ammonia. The biomass-ammonia mixture, if treated in this manner, is rapidly reduced in pressure after discharge and liquid ammonia explosively expands. As a result, the biomass rapidly expands to remove lignin bound to the biomass. Furthermore, the ammonia gas recovery unit separates ammonia gas from the biomass-ammonia mixture discharged by the discharge means and recovers the ammonia gas.